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Weight-Loss Surgery May Lower Colon Cancer Risk

THURSDAY, March 12, 2020 (HealthDay News) -- Obesity increases the risk for colon cancer, but weight-loss surgery may bring the risk back to normal, French researchers report.

People who are obese have a 34% higher risk of colon cancer than the general population, but any type of bariatric (weight-loss) surgery can bring their risk back in line, according to the authors of a new study.

"People aged 50 to 75 are particularly concerned by the risk of developing a colorectal cancer, and all of them should undergo a screening test regularly," said lead researcher Dr. Laurent Bailly of the Centre Hospitalier Universitaire de Nice.

"For individuals with obesity, aged 50 to 75 years, our observational study has shown that bariatric surgery is associated with a decreased risk of colorectal cancer, compared to non-operated patients," Bailly said.

But there's a caveat: This study doesn't prove that weight-loss surgery lowers the risk for colon cancer, only that there is an association.

And the authors of an accompanying journal editorial don't think the findings are conclusive.

"The jury is still out as evidence comes in on whether colorectal cancer risk is increased or decreased after bariatric surgery," said editorial co-author Lance Davidson. He's an associate professor of exercise sciences at Brigham Young University, in Provo, Utah.

"Patients considering surgical interventions for weight loss should weigh their options based on available literature and personal preference to make their decision," Davidson said.

For the study, the French researchers reviewed data collected between 2009 and 2018 on more than 1 million people with obesity aged 50 to 75.

Over five years of follow-up, more than 13,000 developed colon or rectal cancer. Among those who had weight-loss surgery, the colorectal cancer rate was 0.6%. For those who didn't have surgery, it was 1.3%, the findings showed.

The investigators found that fewer cases of colon and rectal cancer were diagnosed after gastric bypass and sleeve gastrectomy procedures than after adjustable gastric banding.

More noncancerous polyps were found after gastric banding than after gastric bypass or sleeve gastrectomy, the researchers reported.

The report was published online March 11 in JAMA Surgery.

The aim of weight-loss surgery is to create a smaller stomach so patients feel full faster and eat less.

In gastric banding, a silicone band is placed around the top of the stomach to make it smaller. With gastric bypass, the stomach is stapled smaller and the small intestine is connected to it. In a sleeve gastrectomy, about 80% of the stomach is removed.

"We've always thought about obesity in terms of diabetes and heart disease and vascular problems, but the truth is, obesity and a rising waist is connected to all chronic disease, not just cardiovascular disease," said Dr. Mitchell Roslin, chief of obesity surgery at Lenox Hill Hospital in New York City. He reviewed the study findings.

Weight-loss surgery improves how much insulin the body makes, which is why many patients' diabetes goes away after surgery, and that could be the reason for the decreased colon cancer risk, Roslin said.

"Insulin resistance and metabolic syndrome and obesity are linked to colon cancer, and people have talked about using the diabetes drug metformin for colorectal cancer," he said.

Roslin said the risk of colon cancer likely rises if patients regain their weight. "But you can buy five to 10 years of life by lowering the risk," he added.

Losing weight may also reduce the risk of other cancers linked to obesity, including uterine cancer and post-menopausal breast cancer, Roslin said.

When people are obese, they also have a high likelihood of insulin resistance. That means they make more insulin, a growth factor for tumors, he noted.

"So, two things are probably occurring," Roslin said. "One, the risk of cancer is probably high and the risk of that cancer being aggressive and difficult to treat is probably also increased, and we know stage-four obese people do worse with cancer than normal-weight people."